eutech-instruments iodide epoxy Manuel D’Utilisation

Instruction Manual 

 

Iodide Electrode

 

 

13

 
The reference electrode must also be considered. When two solutions of different composition are 
brought into contact with one another, liquid junction potentials arise. Millivolt potentials occur 
from the inter-diffusion of ions in the two solutions. Electrode charge will be carried unequally 
across the solution boundary resulting in a potential difference between the two solutions, since 
ions diffuse at different rates. When making measurements, it is important to remember that this 
potential be the same when the reference is in the standardizing solution as well as in the sample 
solution or the change in liquid junction potential will appear as an error in the measured electrode 
potential. 
 
The composition of the liquid junction filling solution in the reference electrode is most important. 
The speed with which the positive and negative ions in the filling solution diffuse into the sample 
should be equitransferent. No junction potential can result if the rate at which positive and negative 
charge carried into the sample is equal. 
 
Strongly acidic (pH = 0-2) and strongly basic (pH = 12-14) solutions are particularly troublesome to 
measure. The high mobility of hydrogen and hydroxide ions in samples make it impossible to mask 
their effect on the junction potential with any concentration of an equitransferent salt. One must 
either calibrate the electrodes in the same pH range as the sample or use a known increment method 
for ion measurement. 
 
 
TROUBLESHOOTING GUIDE 
 
The goal of troubleshooting is the isolation of a problem through checking each of the system 
components in turn: the meter, the glass-ware, the electrodes, the standards and reagents, the 
sample, and the technique. 
 

The meter may be checked by following the check-out procedure in the instrument instruction 
manual. 
 

Clean glassware is essential for good measurement. Be sure to wash the glassware well with a mild 
detergent and rinse very well with distilled or deionized water. Clean glassware will drain without 
leaving water droplets behind. 

The electrode may be checked by using the procedure found in the sections entitled 

Slope Check. 

 

1. 

Be sure to use distilled or deionized water when following the procedures given in 

. 

 
2. 

If the electrode fails to respond as expected, see sections 

 and 

.  Repeat the slope check. 

 
3. 

If the electrode still fails to respond as expected, substitute another iodide ion electrode 
that is known to be in good working order for the questionable electrode. If the problem